Responsive containers (follow-up to #29095) (#29118)

* Follow-up to #29095

This PR fixes the responsive containers that were added in #29095, originally stubbed out in #25631. Apologies to @browner12 for getting that wrong.

Fixes #25631.

* update navbar as well because we cannot reset all containers uniformly

* Update navbars example to include container-xl example to ensure containers match

* rewrite responsive containers docs, add table of max-widths

* Update container docs
- Move table up to the intro
- Remove the container example because it's actually hella confusing
- Update and link to grid example as a demo instead

scss/_grid.scss

@@ -21,9 +21,17 @@
     }
 
     @include media-breakpoint-up($breakpoint, $grid-breakpoints) {
-      .container-#{$breakpoint} {
+      %responsive-container-#{$breakpoint} {
         max-width: $container-max-width;
       }
+
+      @each $name, $width in $grid-breakpoints {
+        @if ($container-max-width > $width or $breakpoint == $name) {
+          .container#{breakpoint-infix($name, $grid-breakpoints)} {
+            @extend %responsive-container-#{$breakpoint};
+          }
+        }
+      }
     }
   }
 }

scss/_navbar.scss

@@ -25,12 +25,23 @@
 
   // Because flex properties aren't inherited, we need to redeclare these first
   // few properties so that content nested within behave properly.
-  > [class^="container"] {
+  %container-flex-properties {
     display: flex;
     flex-wrap: wrap;
     align-items: center;
     justify-content: space-between;
   }
+
+  .container,
+  .container-fluid {
+    @extend %container-flex-properties;
+  }
+
+  @each $breakpoint, $container-max-width in $container-max-widths {
+    > .container#{breakpoint-infix($breakpoint, $container-max-widths)} {
+      @extend %container-flex-properties;
+    }
+  }
 }
 
 
@@ -139,10 +150,21 @@
 
     &#{$infix} {
       @include media-breakpoint-down($breakpoint) {
-        > [class^="container"] {
+        %container-navbar-expand-#{$breakpoint} {
           padding-right: 0;
           padding-left: 0;
         }
+
+        > .container,
+        > .container-fluid {
+          @extend %container-navbar-expand-#{$breakpoint};
+        }
+
+        @each $size, $container-max-width in $container-max-widths {
+          > .container#{breakpoint-infix($size, $container-max-widths)} {
+            @extend %container-navbar-expand-#{$breakpoint};
+          }
+        }
       }
 
       @include media-breakpoint-up($next) {
@@ -163,10 +185,21 @@
         }
 
         // For nesting containers, have to redeclare for alignment purposes
-        > [class^="container"] {
+        %container-nesting-#{$breakpoint} {
           flex-wrap: nowrap;
         }
 
+        > .container,
+        > .container-fluid {
+          @extend %container-nesting-#{$breakpoint};
+        }
+
+        @each $size, $container-max-width in $container-max-widths {
+          > .container#{breakpoint-infix($size, $container-max-widths)} {
+            @extend %container-nesting-#{$breakpoint};
+          }
+        }
+
         .navbar-collapse {
           display: flex !important; // stylelint-disable-line declaration-no-important